In Sway window manager I use titlebars to show which window is active (different colors), no borders at all.

Problem - when there is just one window I want to hide the titlebar.

Almost all issues/posts I find in the internet are about smart hiding borders. But I need something like "smart titlebar". Is it doable?

My current configuration:

default_border normal 0
default_floating_border normal 0
smart_gaps on
gaps inner 3
titlebar_padding 5 1
titlebar_border_thickness 0